sharp map and fwtools cause web server to crush?

I'm building a web application deals with maps using SharpMap and FWTools. I implemented the functionality as web service ( each web service take some arguments and return the URL of an Image). the whale application works fine in debugging mod but when I
run it it (the web server) crush some times. I deployed it to the IIS the IIS crush alwys wher I request the web service. I think the problem in loading some dlls( web server can load those dlls in debugging mod but can't else wise) I'm totaly lost I don't
know what is happening. if you can help any hint could be usefull please.